In recent years, for example, in a manufacturing process of a semiconductor device, the diameter of a semiconductor wafer (hereinafter, referred to as a “wafer”) increasingly becomes larger. Further, the wafer is required to be thinner in a specific process such as mounting. For example, when a thin wafer with a large diameter is transferred or subjected to polishing as it is, warpage or break can occur in the wafer. Therefore, in order to reinforce the wafer, for example, bonding the wafer to a wafer being a supporting substrate or a glass substrate is performed. The predetermined processing such as polishing and the like are performed on the wafer with the wafer being joined with the supporting substrate as described above, and then the wafer and the supporting substrate are separated.
The separation of the wafer and the supporting substrate is performed using, for example, a separation apparatus. For example, a separation apparatus that directly joins a wafer on which devices are formed to a supporting substrate on which a thermally oxidized film is formed and then separates the wafer is proposed in Patent Document 1. The separation apparatus has, for example, a first holder that holds the wafer, a second holder that holds the supporting substrate, and a nozzle that jets liquid between the wafer and the supporting substrate. Then, this separation apparatus separates the wafer and the supporting substrate by jetting liquid between the joined wafer and supporting substrate, namely, to the joint surfaces of the wafer and the supporting substrate from a nozzle at a jetting pressure greater than the joint strength between the wafer and the supporting substrate, preferably, a jetting pressure twice or greater than the joint strength.